Comment on: Butyltin residues in sediment, fish, fish-eating birds, harbour porpoise and human tissues from the Polish coast of the Baltic Sea (Kannan and Falandysz 1997)

Volume 38/Number 1/January 1999

With regard to the so-called Irish proposal, it should be noted that this proposal is not simply an offer of a global whale sanctuary in return for limited commercial coastal whaling. Nor is it 'a compromise deal' as described in your News item. The proposal also includes a ban on international trade in whale products and a phase out of research whaling. It is important to understand that most of the elements of the Irish proposal are either outside of the competence of the IWC or are contrary to the Convention. For example, the regulation of trade is not a matter of competence for the IWC but rather the Convention on Trade in Endangered Species of Wild Fauna and Flora (CITES) or the World Trade Organization (WTO). As another example, limiting whaling to coastal areas and to countries now whaling means that whaling would be prohibited in all the world's oceans except for the coastal areas of Japan and Norway. Clearly, this element of the proposal is contrary to the Convention since there is no scientific basis related to the abundance or distribution of whales for such restric-

tion. The proposal to phase out lethal research is also contrary to the Convention and the rights of signatory nations since the Convention provides for its members to issue permits for the killing of whales for scientific purposes irrespective of anything else in the Conven- tion. While the Irish Commissioner should be applauded for his effort to engage the members of the Commission in discussion aimed at resolving the current deadlock, the point here is that the IWC is empowered (with certain restrictions) to make regulations related to whaling but it is not empowered to make regulations that would amount to amending the Convention.

In summary, Shirley Henderson's news item on the results of the IWC's 50 th Annual Meeting is incom- plete, inaccurate, and highly biassed. Your refiders deserve more objective reporting of news.

DAN GOODMAN Councillor

The Institute of Cetacean Research Tokyo

PII: S0025-326X(98)00068-X

Marine Pollution Bulletin, Vol. 38, No. 1, pp. 57-61, 1999

© 1999 Elsevier Science Ltd. All rights reserved

Printed in Great Britain 0025-326X/99 $ - - see front matter

Comment on: Butyltin Residues in Sediment, Fish, Fish-eating Birds, Harbour Porpoise and Human Tissues from the Polish Coast of the Baltic Sea (Kannan and Falandysz 1997) SUE ROBINSONt, J. VOLOSIN, J. KEITHLY and R. CARDWELL Parametrix Inc., 5808 Lake Washington Boulevard NE, Kirkland, WA 98033, USA

In their March 1997 article, Kannan and Falandysz (1997) provide information on concentrations of butyltin compounds in specific tissues of fish, harbour porpoises (Phacoena phocoena), piscivorous birds, and humans from the Polish coast of the southern Baltic Sea. Their data provide relative measures of butyltin contamination and accumulation potential in species

tAuthor to whom correspondence should be addressed.

inhabiting this area. The authors also use concentrations in fish to conclude that risks may be significant for humans consuming seafood in Poland, thus warranting the establishment of tolerable intakes and fish consumption advisories for butyltins. We disagree with and reexamine their inferences concerning risks.

Specific issues addressed in this article include: (1) the need for the seafood consumption advisory suggested by Kannan and Falandysz (1997); and (2) the comparability of human health risks based on the total

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butyltin data from Kannan and Falandysz (1997) to risks computed using more conventional assumptions, including tributyltin (TBT) concentrations from market basket studies conducted in the United States.

Need for Fish Consumption Advisories in Poland

Using a per capita ingestion rate for Poles, the maximum concentration identified for total butyltins in 1 of 12 composite samples analyzed, and a Tolerable Daily Intake (TDI) derived for TBT, Kannan and Falandysz (1997) conclude that concentrations in fish tissue are potentially harmful to Poland's fish consuming public. There are several questions associ- ated with the approach used to arrive at this conclusion. First, in supporting their assertion of potential risk, the authors use a daily intake derived from the maximum concentration observed in only 1 of 12 composite fish samples.* It is unrealistic to assume that an individual could consume the maximum concentration each day of the year over an indefinite period.

The use of a maximum concentration in estimating dietary exposures is contrary to the state of practice in health risk assessment. Though the convention for estimating exposure concentrations varies by agency, it is typically estimated using either a mean concentration (European Commission, 1996) or an upper confidence limit on the mean (Sydney Water Corporation, 1995; USEPA, 1989a). Because it is a chronic intake that is being estimated for a population consuming fish over time, it is inappropriate to use the maximum value from a data set and conclude that this is what a fish consumer would encounter from Gdansk Bay on a long-term basis. Use of a maximum concentration is only justifiable for assessing risks from acute (short- term) exposures, where consuming a maximum concentration on a few occasions is statistically probable.

Second, the authors make a pivotal assumption in their analysis by comparing the intake rate of total butyltins (i.e., the sum of monobutyltin (MBT), dibutyltin (DBT), and TBT) with a TDI derived specifically for TBT. This raises obvious questions regarding the appropriateness of directly comparing these quantities and the implications of doing so. Regarding the former, the scientific literature indicates that concentrations of all three butyltins can occur in the tissues of marine organisms as a result of in vivo metabolic processes (Krone et al., 1991; Lee, 1985), and that the relative percentages of dominant butyltins (DBT versus TBT) can vary among aquatic species (Krone et al., 1991). For example, in some species of fish, DBT may be the dominant butyltin residue (Krone et al., 1991). Kannan and Falandysz (1997) clearly recognize in their article that there is sequential

*Each composite was comprised of a discrete and variable number of fish. The authors collected data on 58 different specimens comprising nine species.

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Marine Pollution Bulletin

debutylation of TBT to MBT - - a less toxic form - - in frozen tissue stored over time. Though not pointed out in the Kannan and Falandysz analysis, the impact of this assumption may be that the risk posed to seafood consumers by TBT may be less than suggested.

The authors' comparison of total butyltin intake with a TBT TDI also represents an overstatement of the potential toxicity of TBT from the consumption of fish and ignores the different modes of toxic action and dose-response functions for these three compounds. The toxicities of these compounds have been reviewed previously (WHO, 1980, 1990; Nicklin and Robson, 1988; Boyer, 1989) and are known to differ. For example, immunotoxicity (the basis for the TDI used by Kannan and Falandysz and us) following subchronic and chronic exposures has been identified as one sensi- tive toxicological endpoint for TBT (WHO, 1990; USEPA, 1997), and for DBT following subchronic exposures (Summer et al., 1996), but not for MBT (Summer et al., 1996). However, the relative propor- tions of TBT, DBT, and MBT were not established in the fish tissues analyzed by Kannan and Falandysz (1997) analysis. Given data in the scientific literature suggesting MBT, DBT, and TBT differ in toxicity, and differences in butyltin speciation in aquatic species pointed out above, comparison of total butyltin intakes with a threshold dose (TDI) for TBT appears inappropriate.

Another question regarding the Kannan and Falan- dysz analysis concerns the assumed per capita Polish seafood ingestion rate. It may differ from the actual consumption rate for Gdansk Bay fish, where most of their specimens were collected. Owing to the wide variation in consumption patterns for fish and shellfish worldwide, it is generally accepted that local seafood ingestion rates be determined from survey data most applicable to the location of interest, or that site- specific surveys be conducted to determine local consumption patterns (WHO, 1990; Hattemer-Frey and Lau, 1996; Ebert et al., 1994; USEPA, 1989b). Though not acknowledged by the authors, exposure to chemicals in seafood can occur through both recrea- tionally and commercially obtained fish. This means that an individual can potentially receive exposure to butyltin compounds from locally caught fish (self, commercial) as well as from fish caught commercially elsewhere; it would be unusual, however, for an individual to obtain all fish from a single location (e.g., Gdansk Bay) and therefore inappropriate to extrapo- late risk predictions to the general Polish population using this assumption. Recent European risk assessment guidance for existing and new substances (European Commission, 1996) assigns a value no greater than 50 percent to represent the fraction of fish caught from a local water body; the remaining percentage derives from regional sources.

Given the chemical, toxicological and exposure issues identified above, significant uncertainty is associ-


ated with the analysis of potential risk to seafood consumers reported by Kannan and Falandysz (1997). Therefore, their statements regarding the need for establishing tolerable levels and fish consumption advisories in Poland are speculative and uncertain.

Comparability of Seafood Consumption Risks Using Gdansk Bay and Other Market Basket Data

To place health risks from seafood consumption in context, risks were further examined for the following: (1) seafood consumption using data from a United States market basket survey and the assumptions of Kannan and Falandysz (1997); and (2) revised seafood consumption risks using the Kannan and Falandysz (1997) data and exposure assumptions suggested herein.

Market basket TBT seafood risks The data evaluated are from market basket samples

collected in 1989-1990 from various locations throughout the United States (Cardwell et al., in preparation). The period sampled was near the peak usage of TBT-based boat antifoulant paints. Commer- cial seafood markets were sampled randomly and tissues of various species analyzed for TBT. Nearshore rather than offshore species were purchased and analyzed assuming nearshore species would possess higher TBT residues given their closer proximity to sources of TBT (Hall et al., 1987; Langston et al., 1987). Samples included marine bottom fish, marine crustacea, marine bivalve mollusks, freshwater fish, and maricultured salmon. Risks from consuming each type of seafood were evaluated separately.

In our analysis, potential risks were quantified as a hazard quotient (HQ) by comparing the TBT dose (exposure dose) from seafood consumption to the TBT Tolerable Daily Intake, as shown in eqn (1):

Hazard quotient

Seafood exposure dose (mg/kg B W - day)

Tolerable daily intake (mg/kg B W - d a y )

(1)

Exposure assessment With the exception of the tissue concentration used*

the US market basket data were evaluated using the same exposure assumptions used by Kannan and Falandysz (1997). Kannan and Falandysz (1997)

*Conventions for estimating medium-specific exposure concentrations vary. The arithmetic mean concentration is used in these evalu- ations, which is consistent with European Risk Assessment Guidelines (European Commission, 1996). Another common convention is to use an upper 95th percentile confidence interval on the arithmetic mean concentration (Sydney Water Corporation, 1995; USEPA, 1989a). The latter provides an upper bound estimate on the expected environmental concentration.

estimated TBT daily intake for Polish seafood consumers assuming the following: bodyweight for an adult (60 kg), 50 g fish consumed daily. The daily TBT exposure dose (mg/kg/day) from seafood consumption was estimated using a standard exposure model (USEPA, 1989a, b; Sydney Water Corporation, 1995), as shown in eqn (2):

CS x IR x E F x ED Exposure dose = (2)

BW × AT

where

CS = mean chemical concentration in seafood (the mean TBT concentration, mg/kg),

IR = seafood ingestion rate (0.050 kg seafood/day), EF = exposure frequency (365 days/year), ED = exposure duration (30 years), A T = averaging time (exposure duration x 365 days/

year), and B W = body weight (60 kg).

The seafood ingestion rate, exposure frequency and body weight (BW) are the same as those assumed by Kannan and Falandysz (1997).

Tolerable daily intake The TDI of 2.5 E-4 mg/kg BW-day (tributyltin oxide)

is the same value (Penninks, 1993) cited in the Kannan and Falandysz analysis. The TDI represents a No-Observed-Adverse-Effect-Level (NOAEL) for a toxicological endpoint of decreased immune response in rats ingesting TBTO over a period of 18 months. A safety factor of 100 is incorporated in the TDI as an added margin of safety (Penninks, 1993) because the rodent data are extrapolated to humans.

Risk assessment As indicated in Table 1, calculated exposure doses

from daily seafood consumption of fish from the US market were below the TDI for each seafood type examined. In comparison, Kannan and Falandysz estimate a maximum daily intake of 22800 ng/kg butyltin (based on the maximum Gdansk Bay fish tissue concentration). This intake is compared with an ~tcceptable' TDI of 15000 ng/kg.* Given the conservative assumptions in the Kannan and Falandysz analysis, the magnitude of the TDI exceedance (a value of 1.5) is not substantial and suggests that actual risks from TBT (versus total butyltins) would likely be lower.

Revised risks from consumption of Gdansk Bay fish Using the mean concentration of butyltin in Gdansk

Bay fish, and assuming that a maximum of 50 per cent of the fish regularly consumed by the Polish public come from Gdansk Bay (still a conservative assump-

*Note that both the TDI of 15000 ng/kg and the TDI of 2.5 E-04 mg/kg BW-day are equivalent. The former value is expressed in ng/kg based on a 60 kg BW.

59

TABLE 1

Results of United States market basket risk assessment.

Marine Pollution Bulletin

Seafood type Exposure dose (mg/kg BW-day) TDI (mg/kg BW-day) HQ*

Bottom fish 3.4 E-06 2.5 E-04 0.01 Crustaceans 1.1 E-06 2.5 E-04 0.004 Freshwater fish 3.8 E-06 2.5 E-04 0.02 Mollusks 2.6 E-06 2.5 E-04 0.01 Maricultured salmon 8.1 E-06 2.5 E-04 0.03

*An HQ value less than a value of 1 implies that the exposure dose is less than the TDI and no risks would be expected.

tion), an exposure dose of approximately 6 E-05 mg/kg BW-day is estimated (1.1 E-04 mg/kg BW-day if the upper 95th per cent confidence interval on the mean is used). This value is below the TDI of 2.5 E-04 mg/kg BW-day (e.g. an HQ of approximately 0.2), and the true value likely would be lower because the Gdansk Bay fish tissue concentration is based on total butyltins.

We also evaluated the total dose of butyltins to Polish seafood consumers for fish obtained from sources other than Gdansk Bay (e.g., the remaining 50 per cent of their seafood). We assumed that the concentration of TBT in these fish is approximated by the median seafood concentration of TBT of fish sampled recently from the North and Baltic Seas (Keithly et al., in preparation). The combined total butyltin dose to a seafood consumer for fish consumed from both Gdansk Bay and other markets is approximately 7.1 E-05. This equates to an HQ value of approximately 0.3; well below a level of concern. These collective data suggest that risks from butyltin exposure to consumers of seafood from Gdansk Bay and other locations do not approach levels warranting concern to the Polish public.

Conclusion

Several questions are raised following review of the recent analysis conducted by Kannan and Falandysz (1997) in which they suggest that a fish consumption advisory be issued for the Polish seafood consuming public. These questions include: (1) the appropriateness of using the maximum observed fish tissue concentration for butyltins in estimating a chronic intake for the fish-consuming public in Poland; (2) how realistic is it to assume that the majority of fish consumed by the public comes from Gdansk Bay; and (3) is the analysis overly conservative in using total butyltin tissue data to assess risk based on TBT toxicity data? Given these questions, the magnitude of the TDI exceedance for butyltin reported by Kannan and Falandysz (1997) is questionable and uncertain, considering the number of conservative assumptions and the safety factor of 100 already factored into the TDI. An analysis of fish avail- able to seafood consumers in the United States indicates that risks from TBT (versus total butyltins) are well below a level of concern. Further, re-analysis of Kannan and Falandysz' Gdansk Bay fish tissue data

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using more conventional exposure assumptions suggests TBT does not pose a health risk to seafood consumers in Poland. Thus, the health advisory for seafood consumption suggested in their article appears unwarranted.

We appreciate the assistance of Dr Terry Wade, Texas A & M University, for analysis of TBT residues in seafood, as part of the US market basket survey. Reviews of the manuscript were kindly provided by Drs D. Cragin, C. Farr, and H. Schweinfurth.

Boyer, 1. J. (1989) Toxicity of dibutyltin, tributyltin and other organotin compounds to humans and to experimental animals. Toxicology 55, 253-298.

Cardwell, R. D., Keithly, J. C. and Simmonds, J. (in preparation) Tributyltin in market-bought seafood in the United States and estimated human health risks.

Ebert, E. S., Price, P. S. and Keenan, R. E. (1994) Selection of fish consumption estimates for use in the regulatory process. Journal of Exposure Analysis and Environmental Epidemiology 4, 373-393.

European Commission (1996) Technical Guidance Document in Support of Commission Directive 93/67/EEC on Risk Assessment for New Notified Substances and Commission Regulation (EC) No 1488/94 on Risk Assessment for Existing Substances. Part II. Office for Official Publications of the European Communities, Luxembourg.

Hall, L. W. Jr., Lenkevich, M. J., Hall, W. S., Pinkney, A. E. and Bushong, S. J. (1987) Evaluation of butyltin compounds in Maryland waters in Chesapeake Bay. Marine Pollution Bulletin 18(2), 78-83.

Hattemer-Frey, H. A. and Lau, V. (1996) Site-specific considerations in risk assessment. In Environmental Impact of Chemicals: Assessment and Control, eds M. D. Quint, D. Taylor, and R. Purchase. Royal Society of Chemistry, Information Services, Cambridge, 1996, p. 139.

Kannan, K. and Falandysz, J. (1997) Butyltin residues in sediment, fish, fish-eating birds, harbour porpoise, and human tissues from the Polish coast of the Baltic Sea. Marine Pollution Bulletin 34(3), 203-207.

Keithly, J., Henderson, D., Cardwell, R. and Robinson, S. (in preparation) Tributyltin in seafood from Asia, Europe, and North America and an assessment of human health risks.

Krone, C. A., Chan, S. and Varanasi, U. (1991). Butyltins in sediments and benthic fish tissues from the east, Gulf and Pacific coasts of the United States. In Oceans '91, Proceedings, Vol. 2, 1-3 October 1991, Honolulu, Hawaii, pp. 1054-1059.

Langston, W. J., Burt, G. R. and Zhou, M. (1987) Tin and organotin in water, sediments, and benthic organisms of Poole Harbour. Marine Pollution Bulletin 18(12), 634-639.

Lee, R. F. (1985) Metabolism of tributyltin oxide by crabs, oysters, and fish. Marine Environmental Research 17, 145-148.

Nicklin, S. and Robson, M. W. (1988) Organotins: toxicology and biological effects. Applied Organometallic Chemistry 2, 487-508.

Penninks, A. H. (1993) The evaluation of data-derived safety factors for bis(tri-n-butyltin) oxide. In Scientific Evaluation of the Safety Factor for the Acceptable Daily Intake, eds R. Kroes, I. Munro, and E. Poulsen. Taylor and Francis, New York, pp. 351-361.

Summer, K. H., Klein, D., and Greim, H. (1996) Ecological and Toxicological Aspects of Mono- and Disubstituted Methyl-, Butyl-, Octyl- and Dodecyltin Compounds. Prepared for the Organotin Environmental Programme (ORTEP) Association, The Hague, The Netherlands.


Sydney Water Corporation (1995) Methods for Ecological and Human Health Risk Assessment of Chemicals in Sewage Discharge. Sydney Water Corporation, Clean Waterways Unit, New South Wales.

USEPA (1997) Toxicological review. Tributyltin oxide. In Support of Summary Information on the Integrated Risk Information System, July 1997. United States Environmental Protection Agency, Washington, D.C.

USEPA (1989a) Risk Assessment Guidance for Superfund, Vol. 1: Human Health Evaluation Manual (Part A). EPA/540/1-89/002. United States Environmental Protection Agency, Washington, D.C.

USEPA (1989b) Assessing Human Health Risks from Chemically Contaminated Fish and Shellfish: A Guidance Manual. EPA- 503/8-89-002. Office of Marine and Estuarine Protection (WH-556F), United States Environmental Protection Agency, Washington, D.C.

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PII: S0025-326X(98)00168-4

Marine Pollution Bulletin. Vol. 38, No. 1, pp. 61-63, 1999 © 1999 Elsevier Science Ltd. All rights reserved

Printed in Great Britain 0025-326X/99 -- see front matter

Response to the Comment on: Butyltin Residues in Sediment, Fish, Fish-eating Birds, Harbour Porpoise and Human Tissues from the Polish Coast of the Baltic Sea KURUNTHACHALAM KANNAN*§ and JERZY FALANDYSZt "213 National Food Safety and Toxicology Center, Michigan State University, East Lansing, MI 48824, USA tDepartment of Environmental Chemistry and Ecotoxicology, University of Gda~sk, Sobieskiego 18, PL 80-952 Gda~sk, Poland

Tributyltin (TBT) and its derivatives, mono- (MBT), and di- (DBT) butyltin, accumulate in fish and shellfish from coastal areas with boating activities. Despite the reports of their occurrence in seafood (Short and Thrower, 1986; Suzuki et al., 1992; Forsyth and Cl6roux, 1991; Kannan et al., 1995a,b,c, 1996, 1997a,b), few studies have estimated human intake rates. Considering the immunotoxic potential of TBT and DBT, and their exposure to humans via seafood consumption, estimates of dietary intake rates and risks, if any, are needed. Kannan and Falandysz (1997) measured butyltins in fish from the Polish coast of the Baltic sea (first report to measure butyltins in the southern Baltic Sea biota) and noticed their presence at considerable concentrations. Based on the concentrations measured in fish, and fish ingestion rates of Poles, average daily intakes of butyltins were estimated and compared with the reported tolerable daily intake (TDI). Robinson et al.'s (see the previous report) comment is solely based on the following statements in

§Corresponding author.

our article (Kannan and Falandysz, 1997): 'Based on the average daily fish consumption per capita by Poles of 50 g (FAO, 1991), the estimated daily intake of butyltins is in the range of 77022,800 ng person-1. The upper value exceeds the tolerable daily intake (TDI) of 0.25 mg kg bw-I day-1 (Penninks, 1993) i.e. for an individual weighing 60kg, the TDI would be 15,000 ngday-1. This suggests the need for establishing maximum tolerable levels and consumption advisories for butyltins in fish in Poland'. To our knowledge, the above statements have been carefully phrased based on the results of butyltin concentrations in fish flesh, and meticulously thought based on our experience in food safety and toxicology issues for the past 10 [KK] to 25 years [JF].

Robinson et al.'s comments are naive, and indicate their lack of understanding in issues pertaining to fish consumption advisories. Fish consumption advisories are established when a contaminant of concern is present at a concentration above which toxic effects could occur. The consumption advisory can be species- specific since certain species accumulate toxic contami-

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Documents

Comment on: Butyltin residues in sediment, fish, fish-eating birds, harbour porpoise and human tissues from the Polish coast of the Baltic Sea (Kannan and Falandysz 1997)